1. Field of the Invention
This invention relates to a method of determining the orientation of an image of a human body recorded in the form of digital image signal in a radiation image recording medium, and more particularly to a method of determining whether the recorded image of the human body is in the normal position where the body extends in the longitudinal direction of the rectangular field of the image or it extends in the lateral direction thereof.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet or simply as a sheet) is first exposed to a radiation passing through an object to have a radiation image of the object stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, and the radiation image of the object is reproduced as a visible image by use of the image signal on a recording material such as a photographic film, a display device such as a cathode ray tube (CRT), or the like.
In the above-described system, when a radiation image information of the chest of a human body is recorded on a stimulable phosphor sheet, for example, the human body is normally recorded in the direction in which the human body extends in the longitudinal direction of the rectangular stimulable phosphor sheet, and the image constituted by the image signal obtained by read-out of the image signal from the sheet is handled as extending in the longitudinal direction of the sheet even when it is reproduced.
However, it sometimes happens that the human body is recorded in the direction lateral to the sheet, that is the human body extends lateral to the longitudinal direction of the rectangular stimulable phosphor sheet. In such a case, the image read out of the sheet presents an image of the human body extending in the lateral direction of the sheet. In other words, the image signal read out in the same order as that of the normal image provides an image in which the vertical direction of the vertically oriented rectangular sheet is perpendicular to the direction in which the human body extends whereas the vertical direction of the sheet is normally parallel to the direction in which the human body extends.
In the above-described system, the image signal is subject to an image processing or image reproduction as on a CRT. Since the image signal is generally processed on the premise that the vertical direction of the image is in the vertical direction of the human body, it is necessary to change the program of the image processing when the direction of the image is not in the normal direction. For example, various algorisms of the image processing are designed for the image vertically oriented and the output process of the image reproduction system for visualizing the image on a CRT is also designed for the vertically oriented image. Therefore, when the image is not vertically oriented and horizontally oriented, it is necessary to change the algorism of image processing and the output process of image reproduction. In order to change the program like this, it is necessary to know whether the image is in the normal or vertical position or orientation or it is in the horizontal orientation.